Coating system including oxide nanoparticles in oxide matrix

ABSTRACT

In some examples, an article may include a substrate and a coating on the substrate. The substrate may include a superalloy, a ceramic, or a ceramic matrix composite. The coating may include a layer comprising a matrix material and a plurality of nanoparticles. The matrix material may include at least one of silica, zirconia, alumina, titania, or chromia, and the plurality of nanoparticles may include nanoparticles including at least one of yttria, zirconia, alumina, or chromia. In some examples, an average diameter of the nanoparticles is less than about 400 nm.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/879,963, entitled, “COATING SYSTEM INCLUDING OXIDE NANOPARTICLES INOXIDE MATRIX,”, and filed Oct. 9, 2015, which claims the benefit of U.S.Provisional Application No. 62/061,986, titled, “COATING SYSTEMINCLUDING OXIDE NANOPARTICLES IN OXIDE MATRIX,” filed Oct. 9, 2014, theentire content of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to coatings for superalloy substrates, ceramicsubstrates, or ceramic matrix composite substrates.

BACKGROUND

Gas turbine engines include compressor blades that rotate to compressinlet gases and turbine blades that rotate to harness energy fromexpansion of outlet gases. Gas turbine engine blades are attached to gasturbine engine disks. The gas turbine engine disks rotate with the gasturbine engine blades and may experience peak stresses in excess ofabout 1000 megapascals (MPa) due to centrifugal loading from the gasturbine engine blades and weight of the gas turbine engine disksthemselves.

In some examples, gas turbine engine disks may not be directly exposedto the flow path of hot gases in the gas turbine engine. Thus, in someimplementations, maximum surface temperatures of the gas turbine enginedisks may be about 650° C. The thermal and mechanical stresses to whichthe gas turbine engine disks are exposed impose design criteria whichthe alloys that form the gas turbine engine disks may satisfy. Thesedesign criteria include relatively high yield strength and tensilestrength to inhibit yield and fracture of the gas turbine disk,relatively high ductility and fracture toughness to impart tolerance todefects, relatively high resistance to initiation of fatigue cracks, andrelatively low fatigue crack propagation rates. In some implementations,gas turbine disks may be formed from nickel (Ni)-based superalloys,which may satisfy at least some of these design criteria.

In some examples, gas turbine engines may include some components formedfrom alloys and some components formed from ceramics or ceramic matrixcomposites (CMCs). The alloy components and ceramic or CMC compositesmay contact each other.

SUMMARY

The disclosure describes an article that includes a substrate and acoating including a layer including oxide nanoparticles in an oxidematrix. The oxide matrix may include a ceramic material, such as atleast one of silica, zirconia, alumina, titania, or chromia. Similarly,the oxide nanoparticles may include ceramic nanoparticles, such as atleast one of yttria, zirconia, alumina, or chromia. In some examples,the chemical composition of the oxide nanoparticles may be differentfrom the chemical composition of the oxide matrix, which may result inthe oxide nanoparticles forming a second, distinct phase in the firstphase of the oxide matrix.

In some examples, the article includes a gas turbine engine disk, e.g.,a compressor disk or a turbine disk. The coating may be applied to oneor more portions of the gas turbine engine disk, such surfaces of thefir tree recess, a surface of a diaphragm of the gas turbine enginedisk, or a surface of an outer rim of the gas turbine engine disk. Thecoating may be a wear-resistant coating or provide hot corrosionprotection, oxidation protection, or both to the gas turbine enginedisk.

In some examples, a system may include an alloy component in contactwith a ceramic or CMC component. One or both of the alloy component mayinclude the coating that includes alternating layers including amorphousmicrostructure. The coating may be on the alloy component, the ceramicor CMC component, or both, at portions of the component(s) that contacteach other. In some examples, the coating may reduce or substantiallyprevent diffusion of silicon from the ceramic or CMC component into thealloy component.

In some examples, the disclosure describes an article including asubstrate and a coating on the substrate. In accordance with theseexamples, the coating may include a layer including a matrix materialand a plurality of nanoparticles. In some examples, the matrix materialmay include at least one of silica, zirconia, alumina, titania, orchromia, and the plurality of nanoparticles may include nanoparticlescomprising at least one of yttria, zirconia, alumina, or chromia. Anaverage diameter of the nanoparticles may be less than about 400 nm.

In some examples, the disclosure describes a system including a firstcomponent including an alloy substrate and a second component includinga ceramic or a CMC substrate. In accordance with these examples, atleast a portion of the first component is in contact with at least aportion of the second component, and the at least a portion of the firstcomponent, the at least a portion of the second component, or bothcomprises a coating. In some examples, the coating may include a layerincluding a matrix material and a plurality of nanoparticles. In someexamples, the matrix material may include at least one of silica,zirconia, alumina, titania, or chromia, and the plurality ofnanoparticles may include nanoparticles comprising at least one ofyttria, zirconia, alumina, or chromia. An average diameter of thenanoparticles may be less than about 400 nm.

In some examples, the disclosure describes a method including applying alayer of a sol comprising an oxide matrix precursor and a plurality ofnanoparticles by at least one of air spraying, spin coating, or dipcoating. In some examples, the oxide matrix precursor may include aprecursor of at least one of silica, zirconia, alumina, titania, orchromia, and the plurality of nanoparticles may include at least one ofyttria, zirconia, alumina, or chromia. The method also may includecuring the layer to form a gel, and sintering the layer to form a layercomprising an oxide matrix and the plurality of nanoparticles, whereinthe oxide matrix comprises at least one of silica, zirconia, alumina,titania, or chromia.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating a cross-sectional view of anexample article that includes a gas turbine engine disk and a gasturbine engine blade.

FIG. 2 is a conceptual diagram illustrating a cross-sectional view of anexample article that includes a substrate and a coating including alayer including oxide nanoparticles in an oxide matrix.

FIG. 3 is a conceptual diagram illustrating a cross-sectional view ofanother example article that includes a substrate and a coatingincluding a layer including oxide nanoparticles in an oxide matrix.

FIG. 4 is a conceptual and schematic block diagram of a system includinga first component and a second component that may come into contact witheach other.

FIG. 5 is a flow diagram illustrating an example technique for forming acoating using a sol-gel.

DETAILED DESCRIPTION

The disclosure describes an article that includes a substrate and acoating including a layer including oxide nanoparticles in an oxidematrix. The oxide matrix may include a ceramic material, such as atleast one of silica, zirconia, alumina, titania, or chromia. Similarly,the oxide nanoparticles may include ceramic nanoparticles, such as atleast one of yttria, zirconia, alumina, or chromia. In some examples,the chemical composition of the oxide nanoparticles may be differentfrom the chemical composition of the oxide matrix, which may result inthe oxide nanoparticles forming a second, distinct phase in the firstphase of the oxide matrix.

The chemical composition of the oxide nanoparticles may be selected toprovide or modify predetermined properties of the layer of the coating.For example, the chemical composition of the oxide nanoparticles may beselected to provide or modify at least one of the coefficient of thermalexpansion (CTE) of the layer, the chemical properties of the layer, orthe mechanical properties of the layer. For example, the chemicalcomposition of the oxide nanoparticles may be selected to modify theenvironmental barrier properties provided by the layer to the underlyingsubstrate. In some examples, the chemical composition of the oxidenanoparticles also may be based upon the chemical composition of theoxide matrix, such that any mismatch between the CTE of the oxidenanoparticles and the CTE of the matrix material is not sufficient tocause cracking in the layer at the interface of the oxide nanoparticlesand the oxide matrix.

In some examples, an average diameter of the oxide nanoparticles may beless than about 400 nanometers (nm). The average diameter of the oxidenanoparticles may influence formation of cracks during formation of thelayer. Additionally, in some examples, the layer may be deposited from asol-gel. The size of the nanoparticles may influence the formation andcontrol of the sol-gel.

In some examples, the article includes a gas turbine engine disk, e.g.,a compressor disk or a turbine disk. The coating may be applied to oneor more portions of the gas turbine engine disk, such surfaces of thefir tree recess, a surface of a diaphragm of the gas turbine enginedisk, or a surface of an outer rim of the gas turbine engine disk. Insome examples, the coating may be reduce wear between the gas turbineengine disk and a gas turbine engine blade or vane. In other examples,the coating may provide hot corrosion protection, oxidation protection,or both to the gas turbine engine disk.

In some examples, a system, such as a high temperature mechanicalsystem, may include an alloy component in contact with a ceramic or CMCcomponent. One or both of the alloy component or the ceramic or CMCcomponent may include the coating that includes a layer including anoxide matrix material and a plurality of oxide nanoparticles. Thecoating may be on the alloy component, the ceramic or CMC component, orboth, at portions of the component(s) that contact each other. In someexamples, the coating may reduce or substantially prevent diffusion ofsilicon from the ceramic or CMC component into the alloy component.

FIG. 1 is a conceptual diagram illustrating a cross-sectional view of anexample article 10 that includes a gas turbine engine disk 12 and a gasturbine engine blade 14. In gas turbine engines, turbine blades 14 maybe connected to turbine disks 12 using fir tree connections. In suchconnections, each gas turbine engine blade 14 has a dovetail or bladeroot 16 that is inserted into a fir tree recess 18 formed in gas turbineengine disk 12. The facing sides of blade root 16 and fir tree recess 18have respective serrations 20, which may take the form of projectionsand grooves extending in the direction of insertion of blade root 16into fir tree recess 18. In this way, the fir tree connection mayprevent gas turbine engine blade 14 from flying outwardly from gasturbine engine disk 12 during operation of the gas turbine engine androtation of gas turbine engine blade 14 and disk 12.

Surfaces of blade root 16 and fir tree recess 18 form contact pointsbetween gas turbine engine disk 12 and gas turbine engine blade 14.During operation of the gas turbine engine, gas turbine engine disk 12and gas turbine engine blade 14 may rub against each other at thesecontact points due to relative motion between gas turbine engine disk 12and gas turbine engine blade 14. In some examples, the rubbing betweengas turbine engine disk 12 and gas turbine engine blade 14 at thesecontact points may result in fretting.

In accordance with some examples of this disclosure, a coating may beapplied to a gas turbine engine disk 12. In some examples, the coatingmay be selectively applied to gas turbine engine disk 12 at points ofcontact between gas turbine engine disk 12 and gas turbine engine blade14. For example, the coating may be applied to the surface of fir treerecess 18. The coating may include a layer including an oxide matrixmaterial and a plurality of oxide nanoparticles. For example, the oxidematrix material may include at least one of silica, zirconia, alumina,titania, or chromia. In some examples, the oxide nanoparticles mayinclude at least one of zirconia, yttria, alumina, or chromia.

The coating may be resistant to mechanical wear due to rubbing betweenfir tree recess 18 of gas turbine engine disk 12 and gas turbine engineblade 14. In some examples, this may reduce fretting of gas turbineengine disk 12, gas turbine engine blade 14, or both. In some examples,the coating is selectively not on surfaces of gas turbine disk 12 otherthan the surfaces of fir tree recess 18.

In some examples, instead of or in addition to being on the surface offir tree recess 18, the coating may be applied to other portions of gasturbine engine disk 12. For example, the coating may be applied to aportion of gas turbine engine disk 12 that is exposed to hot gasesduring operation of the gas turbine engine. These portions of gasturbine engine disk 21 may include a diaphragm, an outer rim, or both.In some examples, the coating may provide hot corrosion resistance,oxidation protection, or both to gas turbine engine disk 12.

FIG. 2 is a conceptual diagram illustrating a cross-sectional view of anexample article 30 that includes a substrate 32 coated with a coating34. In some examples, article 30 may be an example of gas turbine enginedisk 12, such as a portion of fir tree recess 18, a diaphragm of gasturbine engine disk 12, or an outer rim of gas turbine engine disk 12.In the example illustrated in FIG. 2, coating 34 includes a singlelayer.

In some examples, substrate 32 may include a superalloy, such as aNi-based or Co-based superalloy. In some examples, substrate 32 includesa Ni-based superalloy suitable for use in a gas turbine engine disk orgas turbine engine spacer. As described above, the superalloy from whicha gas turbine engine disk is formed may satisfy certain design criteria,including, for example, relatively high yield strength and tensilestrength to inhibit yield and fracture of the gas turbine engine disk,relatively high ductility and fracture toughness to impart tolerance todefects, relatively high resistance to initiation of fatigue cracks, andrelatively low fatigue crack propagation rates.

Properties of the superalloy from which substrate 32 is formed may be afunction of the composition of the superalloy and the phase constitutionand microstructure of the superalloy. The microstructure of thesuperalloy may include the grain size of the superalloy and aprecipitate phase composition, size, and volume fraction. In someexamples, the phase constitution and microstructure of the superalloymay be affected by mechanical and thermal processing of the superalloy.For example, thermal processing, e.g., heat treatment, of the superalloymay affect grain structure of the superalloy, precipitate phase sizeand/or composition, or the like.

In some examples, substrate 32 includes a polycrystalline Ni-basedsuperalloy, which includes a plurality of grains. Substrate 32 mayinclude at least one of Al, Ti, or Ta in addition to Ni. In someexamples, a concentration of elements, such as between about 2 weightpercent (wt. %) and about 5 wt. % Al, between about 2 wt. % and about 5wt. % Ti, and less than about 3 wt. % tantalum (Ta), in substrate 32 maybe sufficient to result in gamma-prime (γ′) precipitate formation insubstrate 32. For example, the concentration of Al, Ti, and/or Ta insubstrate 32 may result in a γ′ precipitate phase volume fractionbetween about 40 volume percent (vol. %) and about 55 vol. %. In someinstances, higher or lower elemental contents of the individual gammaprime forming elements can be employed while maintaining the overallgamma prime phase fraction at desired levels for properties such asstrength and ductility. The volume fraction, size, and distribution ofthe γ′ precipitate phase may be influenced by the alloy composition,heat treatment temperature, heat treatment duration, and cooling rateduring heat treatment. Additionally, substrate 32 may include grainsizes between about 5 micrometers (μm) in diameter to between about 30μm and about 50 μm or more in diameter, engineered for a combination ofyield strength, resistance to fatigue crack initiation, creep strength,and resistance to fatigue crack growth. In some examples, substrate 32may include additional elements that segregate to grain boundaries ofsubstrate 32. The segregating elements may affect creep resistance andlow-cycle fatigue resistance of substrate 32. Examples of segregatingelements include boron (B; up to about 0.03 weight percent (wt. %) ofsubstrate 12), carbon (C; up to about 0.05 wt. % of substrate 32), andzirconium (Zr; up to about 0.1 wt. % of substrate 32). Examples ofcompositions and heat treatment techniques that may result in suitableNi-based disk alloys are described in U.S. patent application Ser. No.12/755,170, entitled “TECHNIQUES FOR CONTROLLING PRECIPITATE PHASEDOMAIN SIZE IN AN ALLOY,” and filed Apr. 6, 2010, the entire content ofwhich is incorporated herein by reference.

In an example, substrate 32 may include a Ni-based superalloy with acomposition of about 15 wt. % Cr, about 18.5 wt. % Co, about 5 wt. % Mo,about 3 wt. % Al, about 3.6 wt. % Ti, about 2 wt. % Ta, about 0.5 wt. %Hf, about 0.06 wt. % Zr, about 0.027 wt. % C, about 0.015 wt. % B, and abalance Ni (about 52.3 wt. % Ni).

Example superalloys include RR1000 (a Ni-based superalloy containingabout 52.4 mass percent (mas. %) Ni, about 15 mas. % Cr, about 18.5 mas.% Co, about 5 mas. % Mo, about 3.6 mas. % Ti, about 3 mas. % Al, about 2mas. % Ta, about 0.5 mas. % Hf, and about 0.03 mas. % C); UDIMET® alloy720, available from Special Metals Corporation (a Ni-based alloyincluding between 15.5 and 16.5% Cr, between 14 and 15.5% Co, between2.75 and 3.25% Mo, between 1.00 and 1.50% W, between 4.75 and 5.25 Ti,between 2.25 and 2.75% Al, between 0.01 and 0.02% C, between 0.025 and0.05% Zr, between 0.01 and 0.02% B, and a balance Ni); those availablefrom Martin-Marietta Corp., Bethesda, Md., under the trade designationMAR-M247; those available from Cannon-Muskegon Corp., Muskegon, Mich.,under the trade designation CMSX-3 and CMXS-4; and the like.

In other examples, substrate 32 may include a ceramic or ceramic matrixcomposite. In some examples in which substrate 32 includes a ceramic,the ceramic may be substantially homogeneous. In some examples, asubstrate 32 that includes a ceramic includes, for example, aSi-containing ceramic, such SiO₂, silicon carbide (SiC) or siliconnitride (Si₃N₄); Al₂O₃; aluminosilicate (e.g., Al₂SiO₅); or the like. Inother examples, substrate 32 includes a metal alloy that includes Si,such as a molybdenum-silicon alloy (e.g., MoSi₂) or a niobium-siliconalloy (e.g., NbSi₂).

In examples in which substrate 32 includes a CMC, substrate 32 includesa matrix material and a reinforcement material. The matrix materialincludes a ceramic material, such as, for example, SiC, Si₃N₄, Al₂O₃,aluminosilicate, SiO₂, or the like. The CMC further includes acontinuous or discontinuous reinforcement material. For example, thereinforcement material may include discontinuous whiskers, platelets, orparticulates. As other examples, the reinforcement material may includea continuous monofilament or multifilament weave. In some examples,substrate 32 may include a SiC reinforcement material in a SiC matrixmaterial.

Coating 34 may include a layer (e.g., at least one layer) including anoxide matrix material and a plurality of oxide nanoparticles. The oxidematrix may include at least one ceramic material, such as at least oneof silica, zirconia, alumina, titania, or chromia. In some examples, theoxide matrix may include a mixture of two or more oxides, such as amixture of silica and zirconia. The oxide matrix material may contributeto hot corrosion resistance, oxidation protection, or both, provided bycoating 34 to substrate 32.

The oxide nanoparticles may include ceramic nanoparticles, such as atleast one of yttria, zirconia, alumina, or chromia. In some examples,the oxide nanoparticles may include yttria stabilized with at least oneother oxide, such as at least one of yttria, alumina, or chromia. Insome examples, when the at least one other oxide is present in the oxidenanoparticles, the oxide nanoparticles may include between about 1 wt. %and about 10 wt. % of the at least one other oxide. In some examples,the at least one other oxide may be present in the oxide nanoparticlesin a concentration of about 3 mol. %. In some examples, the chemicalcomposition of the oxide nanoparticles may be different from thechemical composition of the oxide matrix, which may result in the oxidenanoparticles forming a second, distinct phase in the first phase of theoxide matrix.

The chemical composition of the oxide nanoparticles may be selected toprovide or modify one or more predetermined properties of the layer ofthe coating. In some examples, the chemical composition of the oxidenanoparticles also may be based upon the chemical composition of theoxide matrix, such that any mismatch between the CTE of the oxidenanoparticles and the CTE of the matrix material is not sufficient tocause cracking in the layer at the interface of the oxide nanoparticlesand the oxide matrix.

In some examples, the chemical composition of the oxide nanoparticlesmay be selected to modify at least one of the coefficient of thermalexpansion (CTE) of the layer of coating 34. Too large of a mismatchbetween the CTE of coating 34 and substrate 32 may generate stress incoating 34, substrate 32, or both near surface 36 of substrate due todifferential expansion and contraction of substrate 32 and coating 34during thermal cycling. Because of this, it may be beneficial to formcoating 34 of materials that, together, give an effective CTE to coating34 that is sufficiently close to the CTE of substrate 32. For example,the effective CTE of coating 34 may be within about 25% of the CTE ofsubstrate 32. The nanoparticles may have a different CTE than the matrixmaterial, and thus may modify the CTE of coating 34. For example, theCTE of coating 34 may be approximately equal to the volume-weightedaverage CTE of the nanoparticles and the matrix material. In this way,the nanoparticles may facilitate matching or near matching of the CTEsof substrate 32 and coating 34.

In some examples, the chemical composition of the oxide nanoparticlesmay be selected to modify the environmental barrier properties providedby the layer to the underlying substrate. For example, the chemicalcomposition of the oxide nanoparticles may affect the corrosionresistance, oxidation resistance, or both of coating 34.

In some examples, an average diameter of the oxide nanoparticles may beless than about 400 nanometers (nm), such as less than about 100 nm, orabout 90 nm. The average diameter of the oxide nanoparticles mayinfluence formation of cracks during formation of the layer of coating34. Additionally, in some examples, the layer may be deposited from asol-gel. The size of the nanoparticles may influence the formation andcontrol of the sol-gel. Additionally or alternatively, the size of theoxide nanoparticles may affect the mechanical properties of coating 34,such as toughness, crack propagation, or the like. In some examples, theoxide nanoparticles may be disposed throughout coating 34 substantiallyhomogeneously, and substantially no (e.g., no or nearly no)nanoparticles may be agglomerated in clumps of nanoparticles.

As described above, the volume fraction of the oxide nanoparticles incoating 34 also may influence properties of coating 34, including theCTE of coating 34, environmental barrier properties, and the like. Insome examples, the concentration of nanoparticles in the layer ofcoating 34 may be defined based on the concentration of nanoparticles inthe mixture from which the layer is formed. For example, nanoparticlesmay be present in the mixture from which the layer is formed at aconcentration of between about 0.7 volume percent (vol. %) and about 13vol. %, based on the volume of nanoparticles divided by the total volumeof nanoparticles plus matrix material precursor. In some examples, thenanoparticles may be present in the mixture from which the layer ofcoating 34 is formed at a concentration of between about 5 vol. % andabout 7.5 vol. %, based on the volume of nanoparticles divided by thetotal volume of nanoparticles plus matrix material precursor.

In some examples, the plurality of nanoparticles may reduce cracking incoating 34 under stress, such as thermal cycling or contact with anothercomponent, compared to a coating including a homogeneous matrixmaterial.

In some examples, rather than being formed as a single layer, a coatingmay include a plurality of layers. FIG. 3 is a conceptual diagramillustrating a cross-sectional view of another example article 40 thatincludes a substrate 32 and a coating 44 including a plurality of layers46-48.

Substrate 32 may be similar to or substantially the same as substrate 32described with respect to FIG. 2. Similarly, article 40 may be anexample of gas turbine engine disk 12, such as a portion of fir treerecess 18, a diaphragm of gas turbine engine disk 12, or an outer rim ofgas turbine engine disk 12.

Each of plurality of layers 46-48 may include an oxide matrix materialand a plurality of oxide nanoparticles. In some examples, each of layers46 may be of substantially the same chemical composition (for both theoxide matrix material and oxide nanoparticles), with substantially thesame volume fraction of oxide nanoparticles, and the same size of oxidenanoparticles. In other examples, at least one of layers 46-48 may haveat least one property that is different than at least one property of atleast one other of layers 46-48. The properties that may be the same ordifferent between layers 46-48 include the chemical composition of theoxide matrix material, the chemical composition of the oxidenanoparticles, the size of the oxide nanoparticles, the volume fractionof the oxide nanoparticles, the thickness of the layer, or the like.

The properties of each layer of layers 46-48 may be selected to providepredetermined properties to coating 44. For example, the chemicalcomposition of the oxide matrix material, the chemical composition ofthe oxide nanoparticles, and the volume fraction of oxide nanoparticlesmay be selected such that layer 46 in FIG. 3 has a CTE substantially thesame (e.g., the same or nearly the same) as the CTE of substrate 32. Asanother example, the chemical composition of the oxide matrix material,the chemical composition of the oxide nanoparticles, and the volumefraction of oxide nanoparticles may be selected such that layer 48 inFIG. 48 possesses at least one of hot corrosion resistance, oxidationresistance, or wear resistance, depending on the application of coating44.

In some examples, coating 44 may include between 1 layer and about 20layers, such as between 3 layers and 10 layers. Forming coating 44 of aplurality of layers 46-48 may reduce residual stress (e.g., stress dueto the coating process) in coating 44, e.g., compared to forming coating44 of a single thick layer. In some examples, coating 44 may be appliedusing a sol-gel technique. In a sol-gel technique, each of layers 46-48is applied from a slurry, then dried. In examples in which coating 44 isapplied as a single, thick layer, cracking may occur during drying ofcoating 44. Applying coating 44 as a plurality of relatively thinnerlayers 46-48 may reduce or substantially eliminate cracking during thedrying process.

Additionally or alternatively, in some examples, each of layers 46-48may include different compositions. By including layers 46-48 withdifferent compositions, crack mitigation within coating 44 may bereduced, e.g., due to the interfaces between layers 46-48. In someexamples, by forming coating 44 with multiple layers, the thicknesses ofthe individual layers may be reduced while providing the same totalthickness for coating 44.

Coating 34 or 44 may define a total thickness, measured in a directionnormal to surface 36 of substrate 32, of between about 1 micrometers andabout 25 micrometers. For example, coating 34 or 44 may define a totalthickness of between about 1 micrometer and about 10 micrometers. Insome examples, each of layers 46-48 defines a thickness, measured in adirection normal to surface 36 of substrate 32, of between about 0.1micrometer and about 10 micrometers, such as between about 1 micrometerand about 5 micrometers. In some examples, the thickness of each oflayers 46-48 may be substantially the same (e.g., the same or nearly thesame). In other examples, the thickness of at least one of layers 46-48may be different than the thickness of at least another of layers 46-48.

In some examples, coatings 34 or 44 may be resistant to mechanical weardue to rubbing between article 30 or 40, respectively, and anothercomponent. For example, coatings 34 or 44 may be applied on fir treerecess 18 of gas turbine engine disk 12, and may reduce fretting of gasturbine engine disk 12, gas turbine engine blade 14, or both.

In some examples, coatings 34 or 44 may be applied to other portions ofgas turbine engine disk 12. For example, coatings 34 or 44 may beapplied to a portion of gas turbine engine disk 12 that is exposed tohot gases during operation of the gas turbine engine. These portions ofgas turbine engine disk 21 may include a diaphragm, an outer rim, orboth. In some examples, coatings 34 or 44 may provide hot corrosionresistance, oxidation protection, or both to gas turbine engine disk 12.

In some examples, a coating including at least one layer including oxidematrix material and oxide nanoparticles may form a barrier coating atlocations of components that may come into contact with othercomponents. For example, as described with respect to FIGS. 1-3, thecoating may be applied to surface of a fir tree recess 18 of a gasturbine engine disk 12. In some examples, the coating may be applied tosurfaces of other components that may come into contact with a secondcomponent. FIG. 4 is a conceptual and schematic block diagram of asystem 50 including a first component 52 and a second component 58 thatmay come into contact with each other.

First component 52 includes a substrate 54 and a coating 56 on substrate54. Coating 56 includes oxide nanoparticles in an oxide matrix, and mayinclude coating 34 of FIG. 2 or coating 54 of FIG. 3.

Substrate 54 may include any of the materials described above withrespect to FIG. 2. For example, substrate 54 may include a superalloy,such as a Ni-based, Co-based, Ti-based, or Fe-based superalloy. As otherexamples, substrate 54 may include a ceramic material or CMC material.In some examples, in which substrate 64 includes a ceramic material orCMC material, the ceramic material or CMC material may include silicon,either alone or in a compound (e.g., SiC, Si₃N₄, or the like).

Second component 58 also may include any of the materials describedabove with respect to FIG. 2 for substrate 32. For example, secondcomponent 58 may include a superalloy, such as a Ni-based, Co-based,Ti-based, or Fe-based superalloy. As other examples, second component 58may include a ceramic material or CMC material. In some examples, inwhich second component 58 includes a ceramic material or CMC material,the ceramic material or CMC material may include silicon, either aloneor in a compound (e.g., SiC, Si₃N₄, or the like). Although not shown inFIG. 4, in some examples, second component 58 may include a coating on asubstrate.

Substrate 54 of first component 52 and second component 58 may includedifferent chemical compositions. In some examples, substrate 54 mayinclude a superalloy and second component 58 may include a ceramic or aCMC. For example, substrate 54 may include a Ni-based superalloy andsecond component 58 may include a ceramic of a CMC including Si. Inother examples, substrate 54 may include a ceramic of a CMC and secondcomponent 58 may include a superalloy. For example, substrate 54 mayinclude a ceramic of a CMC including Si second component 58 may includea Ni-based superalloy.

Coating 56 may reduce or substantially prevent ingress, such as throughdiffusion, of silicon from the ceramic or the CMC into the superalloy.In some examples, at relatively high operating temperatures (e.g.,greater than about 1400° F. (about 760° C.)) and after relatively longtimes (e.g., greater than about 10,000 hours, nickel and silicon mayreact and degrade properties and performance of a Ni-based superalloy.Thus, by reducing or substantially preventing ingress of Si into thesuperalloy, coating 56 may extend a useful life of the superalloy.

In some examples, system 50 including first component 52 and secondcomponent 58 may be components of a high temperature mechanical system,such as a gas turbine engine. For example, a CMC blade track may be heldby a metallic component, a hybrid turbine vane may include a CMC airfoiland metallic end walls, or a CMC blade may be held by a nickel diskalloy turbine disk.

In some examples, coating 34, 44, and 56 may be formed using a sol-gelcoating technique. FIG. 5 is a flow diagram illustrating an exampletechnique for forming a coating 34, 44, 56 using a sol-gel. Thetechnique of FIG. 5 optionally may include forming a sol is includingprecursors of the coating materials, such as a precursor of the matrixmaterial, in a solvent (62). In other examples, the sol may bepreviously formed. The precursors of the coating materials may berelatively small molecules or particles, and may be in a form that mayform a gel upon further processing. Example coating precursors mayinclude zirconium butoxide, methyltrimethoxysilane, and the like. Insome examples, zirconium butoxide and methyltrimethoxysilane may bemixed with an organic solvent that evaporates relatively easily, such asisopropyl alcohol or ethanol, and, optionally, acetylacetone in a solfor forming a coating including a matrix that includes silica andzirconia. In some examples, the sol may include additional materialsthat facilitate formation of the gel, such as a crosslinking agent, acatalyst, a chemical modifier, such as acetylacetone (which may affectthe reaction rate of precursors in the sol), or the like.

The sol also may include oxide nanoparticles. In some examples, the solincluding the oxide matrix material precursors may be mixed first, thena suspension of oxide nanoparticles may be added to the sol prior toapplying the sol to substrate 32. In some examples, the suspension ofoxide nanoparticles may include the oxide nanoparticles, a solvent, and,optionally, a dispersant. In some examples, the solvent may be thesimilar to or substantially the same as the solvent in the sol. Forexample, the suspension of oxide nanoparticles may include isopropylalcohol as a solvent. In some examples, the dispersant may includepolyethyleneimine.

The sol may be mixed with the suspension of oxide nanoparticles in apredetermined ratio. The ratio may be determined based on a desiredvolume fraction of oxide nanoparticles in the final layer of coating 34,44, and 56.

The sol mixture may be applied to the substrate 32 using, for example,air spraying, spin coating, or dip-coating (64). The sol mixture may beapplied in a layer of a predetermined thickness, which may besubstantially the same as the thickness of the layer (e.g., a layer oflayers 46-48 of coating 44). In some examples, the thickness of thelayer may be greater than the thickness of the coating layer to beformed, as the layer may shrink when cured due to removal of solvent.

In some examples, after applying a layer of the sol mixture, the layermay optionally be cured to form the gel (66). For example, the layer maybe cured at a temperature between about room temperature and about 200°C. for up to about three hours. In some examples, the layer may be curedat a temperature of about 150° C. for about 15 minutes. The curing mayremove substantially all of the solvent(s) from the layer, and, in someexamples, may reduce or substantially eliminate cracking of the layer orcoating 44.

In some examples, as described above, coating 44 may include a pluralityof layers 46-48. For each layer of the layers 46-48, the sol may beapplied (64) and cured (66) before depositing the next layer of layers46-48.

Once at least some of the layers 46-48 have been formed (or a singlelayer in the case of coating 34) (the “YES” branch of decision block68), the layers 46-48 may be sintered to form coating 34, 44, or 56(70). For example, once all of the layers 46-48 have been deposited, thelayers 46-48 may be sintered at a temperature between about 600° C. andabout 1000° C. for between about 1 hour and about 5 hours. As anotherexample, once at least one layer (e.g., one layer or five layers) havebeen deposited, these layers may be sintered, then additional layers maybe deposited, cured, and sintered. In some examples, sintering somelayers prior to depositing additional layers may facilitate formation ofa thicker coating. In some examples, the layers 46-48 may be sintered ata temperature of about 700° C. or about 800° C. for about 1 hour.Sintering may result information of coating 34, 44, or 56 including anoxide matrix and a plurality of oxide nanoparticles.

EXAMPLES Example 1

A coating was deposited on a 1″ diameter RR1000 coin using spin coating.The matrix material was prepared as a sol using a sol-gel technique. Thesolvent for the sol was isopropyl alcohol (IPA), which was mixed withacetylacetone, a chemical modifier, prior to the addition of zirconiumbutoxide (ZrB), a zirconium precursor. ZrB was then added into thesolution, followed by methyltrimethoxysilane (MTMS) while the mixturewas stirred. The molar ratio of acetylacetone to ZrB was 0.25:1. Themolar ratio of IPA to ZrB was 140:1 and the molar ratio of IPA to MTMSwas 19.5:1, such that the final matrix material in the deposited coatingwas 10 mol % ZrO₂ in SiO₂. After all the constituents were added, themixture was mixed for 15 minutes. De-ionized water (DI water) was thenadded to promote hydrolysis of methoxy groups from the MTMS and butoxidegroups from the ZrB to allow free metal hydroxides to condense to form agel. The molar ratio of DI water to total ZrB+MTMS was 5:1. The mixtureincluding the DI water was mixed for 3 minutes, then the mixing wasstopped. The sol was aged in an enclosed container for about 24 hours.

A suspension of yttria stabilized (YSZ) nanoparticles with a nominaldiameter of about 90 nm was also prepared. IPA solvent was mixed withpolyethyleneimine (PEI), a dispersant. The concentration of PEI in themixture was 0.5 wt. %. YSZ particles were then added to the IPA and PEImixture to a concentration of 29.5+/−0.5 wt. %. The mixture was milledin a baffled bottle with zirconia milling media for at least 18 hours atabout 140 rpm to break down agglomerates of nanoparticles in theas-received condition. The suspension was then sonicated using a hornsonifier at an amplitude of 60% for about 38 minutes in an ice bath.About 205.2 μL YSZ suspension per mL of sol was mixed to form the finalmixture used to form the coating. This resulted in a concentration ofYSZ nanoparticles in the mixture of about 7.5 vol. % particles, based onthe total volume of the particles, MTMS, and ZrB.

Prior to spin coating, the final mixture was pipetted onto the RR1000coin until the coin was covered with the final mixture. The RR1000 coinwas then spun at 2000 rpm for 30 seconds. The acceleration was 800 rpmper second. The spun film was cured at a temperature of about 150° C.for about 15 minutes. Five layers were applied in this manner. Afterapplying the fifth layer, the film was sintered at a temperature ofabout 700° C. for about 1 hour. The resultant coating was crack free.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A system comprising: a first component comprising an alloy substratecomprising an alloy substrate coated with a coating, wherein the coatingcomprises a layer comprising an oxide matrix and a plurality of oxidenanoparticles, and wherein: the oxide matrix comprises at least one ofsilica, zirconia, alumina, titania, or chromia; the plurality of oxidenanoparticles comprises at least one of yttria, zirconia, alumina, orchromia; a chemical composition of the plurality of oxide nanoparticlesis different from the chemical composition of the oxide matrix such thatthe plurality of oxide nanoparticles form a second, distinct phase inthe oxide matrix; an average diameter of the plurality of oxidenanoparticles is less than 400 nm; and the layer is formed from amixture that comprises a precursor of the oxide matrix and between about0.7 volume percent and about 13 volume percent of the plurality of oxidenanoparticles, wherein the volume percent of the plurality of oxidenanoparticles is based on the volume of oxide nanoparticles divided by atotal volume of the plurality of oxide nanoparticles plus the precursorof the oxide matrix; and a second component comprising a ceramic or aCMC substrate, wherein at least a portion of the second component is incontact with at least a portion of the coating.
 2. The system of claim1, wherein the mixture from which the layer is formed comprises betweenabout 5 volume percent and about 7.5 volume percent of thenanoparticles.
 3. The system of claim 1, wherein the matrix materialcomprises silica and zirconia.
 4. The system of claim 1, wherein thenanoparticles comprise zirconia stabilized with at least one of yttria,alumina, or chromia.
 5. The system of claim 1, wherein the nanoparticlescomprise yttria-stabilized zirconia.
 6. The system of claim 1, whereinthe coating comprises a plurality of layers, each layer of the pluralitycomprises the matrix material and the plurality of nanoparticles.
 7. Thesystem of claim 6, wherein the coating comprises between 1 and 20layers.
 8. The system of claim 1, wherein the coating defines athickness of between about 0.1 micrometers and about 25 micrometers. 9.The system of claim 1, wherein the first component comprises a gasturbine engine disk and the second component comprises a gas turbineengine blade.
 10. The system of claim 1, wherein the second componentcomprises a gas turbine engine blade track.
 11. A system comprising: afirst component comprising an alloy substrate; and a second componentcomprising a ceramic or a CMC substrate coated with a coating, whereinthe coating comprises a layer comprising an oxide matrix and a pluralityof oxide nanoparticles, and wherein: the oxide matrix comprises at leastone of silica, zirconia, alumina, titania, or chromia; the plurality ofoxide nanoparticles comprises at least one of yttria, zirconia, alumina,or chromia; a chemical composition of the plurality of oxidenanoparticles is different from the chemical composition of the oxidematrix such that the plurality of oxide nanoparticles forms a second,distinct phase in the oxide matrix; an average diameter of the pluralityof oxide nanoparticles is less than 400 nm; the layer is formed from amixture comprising a precursor of the oxide matrix and between about 0.7volume percent and about 13 volume percent of the plurality of oxidenanoparticles, wherein the volume percent of the plurality of oxidenanoparticles is based on the volume of oxide nanoparticles divided by atotal volume of the plurality of oxide nanoparticles plus a precursor ofthe oxide matrix; and at least a portion of the first component is incontact with at least a portion of the coating on the second component.12. The system of claim 11, wherein the mixture from which the layer isformed comprises between about 5 volume percent and about 7.5 volumepercent of the nanoparticles.
 13. The system of claim 11, wherein thematrix material comprises silica and zirconia.
 14. The system of claim1, wherein the nanoparticles comprise zirconia stabilized with at leastone of yttria, alumina, or chromia.
 15. The system of claim 1, whereinthe nanoparticles comprise yttria-stabilized zirconia.
 16. The system ofclaim 1, wherein the coating comprises a plurality of layers, each layerof the plurality comprises the matrix material and the plurality ofnanoparticles.
 17. The system of claim 16, wherein the coating comprisesbetween 1 and 20 layers.
 18. The system of claim 1, wherein the coatingdefines a thickness of between about 0.1 micrometers and about 25micrometers.
 19. The system of claim 1, wherein the first componentcomprises a gas turbine engine disk and the second component comprises agas turbine engine blade.
 20. The system of claim 1, wherein the secondcomponent comprises a gas turbine engine blade track.